Biology of reproduction in planktonic crustaceans of the family Cercopagidae (Polyphemoidae, Cladocera)

At the present time, the species of the family Cercopagidae of the genera Bythotrephes and Cercopagis (Cercopagis) are widespread in the Volga River cascade, the Baltic Sea, and lakes of North America. Like all Cladocera, Bythotrephes and C. (C.) pengoi have periods of parthenogenetic and gamogenetic reproduction with participation of males. Winter eggs are formed in gamogenetic females. The period of parthenogenesis becomes longer in the species from southern water bodies, but that of gamogenesis, in water pools located northward. Newborn parthenogenetic females have a round brood pouch without a point before the second molting. This feature distinguishes these females from other ones in the C. (C.) pengoi population. Cercopagis (Apagis) ossiani, described as an independent species, appears to be a C. (C.) pengoi female hatched from a winter egg. This female has four pairs of claws on the thickened caudal appendage without loop, large size, and the shortened firs pair of thoracic limbs, and maximal fecundity.